# Physics: Post your doubts here!

#### amal sharkawi

Can anyone plz tell me which year is this experiment???
P.3 AS

#### amal sharkawi

Can anyone tell me which year is this ????
AS P.3

#### areeba240

Upthrust is caused by difference in pressure at the top and bottom of the block.
The pressure is due to WATER. Pressure changes with height but since all blocks have the same height and all are in the same fluid thus all blocks will have an equal difference of pressure between the top and bottom. Therefore all of them will experience same Upthrust.

The formula pressure = h × D ×g is for fluids and the density is of the fluid so it's the desnity of liquid that matters NOT the object immersed
thank u

#### i_try9621

Ans is D from 11/M/J/12

View attachment 60723 Ans is D from 11/M/J/12
This is a simple moments question.

Clockwise and anticlockwise moments must be equal for equilibrium. So if distance y is increased, we have to move the pivot to the right so that to cancel out the increase in y.
The pivot here is R . So moving Pivot to the right decreases y and increases x thus reaching an equilibrium.

#### qwertypoiu

View attachment 60723 Ans is D from 11/M/J/12
The force L was moved to the right.
Remember that, for any system to be in equilibrium, two conditions must be satisfied:
1. No net force
2. No net moments

This second condition is violated here by moving the L to the right. But maybe you're wondering, which point should I take as the pivot when I wanna see if there is any net moments or not? The answer is ALL points must have no net moments in order for a system to be in equilibrium. But we can't check all so we usually just choose any and usually the simplest is the center.
So let's take the center.

Before, R was right at the center and so contributed no moment to this central point since its perpendicular distance to it was zero.
And L provided the clockwise moment to this center point, and W countered this with equal but anticlockwise moment.

After L is moved, we are told the system remains in equilibrium. Note that, the actual magnitude of R cannot change. This is in order to preserve the first condition (up = down)
Also, no horizontal forces can act. This again will violate the first condition (left = right)

Keeping the support (the center) as our pivot point, we see that now there is extra clockwise moment caused by L. If R moves to the left, it causes even more clockwise moment. Since we need to counter the extra moment caused by L, R must move to the right. By moving to the right, the perpendicular distance from the pivot of R is no longer zero. It causes a moment in anticlockwise direction because it acts upwards, and thus counters L (along with the help of W)

Alternatively, we can check moments upon another point, the point where force R has started acting on after moving to right. This allows ignoring the effect of R and rather looking at the effects of distance of W and L from the pivot.

#### The Sarcastic Retard

(b) is the doubt.

#### Wolfgangs

How to solve this question?

#### Attachments

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#### Benny Wu

Did anyone here take 2016 May/June paper 13? I would like to know the answer to the questions relating to vector, diffraction and interference.
Or does anyone have this years question papers? THX

How to solve this question?
Force = (momentum)/time or (mv)/t or (m/t)v (They all are the same thing just written differently)
So we have m/t as 90 kg per minute but we have to convert it to seconds.
90/60 = 1.5 kg per second.
Force = (m/t)v = 1.5×20 = 30N.

#### Hassan (SHT)

Someone here who can solve these questions

#### Rizwan Javed

And Q10, is it C?

#### Rizwan Javed

I solved the questions, but not sure my answers are right or wrong so can you please post the answers as XPFMember said

#### Hassan (SHT)

Here are the Answers Q15 B
Q2 B
Q10 C
Q6 C
These Questions are smart enough, haha
I got the same answer for Q6 , I Wonder how gora tricks us